Reference may be made to the well-known Mannheim process involving reaction of MOP with sulphuric acid. The major problem with the process is that it is energy intensive and poses a problem of hydrochloric acid (HCl) management when no application of commensurate volume for HCl is available in the vicinity.
In a paper entitled “Production of potassium sulphate by an ammoniation process”, Chemical Engineer, 349, pp 688-690, October 1979, by J. A. Fernandez Lozano and A. Wint, describes the process of SOP manufacture from MOP through reaction with gypsum in presence of ammonia. The principle of the process is the double decomposition reaction between gypsum and potassium chloride in presence of ammonia at 0° C. The main disadvantage of the process is that it is energy intensive and necessitates careful design of the reactor for safe operation. In a paper entitled “Messo pilots new potassium sulphate process', Phosphorous & Potassium, 178, March-April 1992, p-20, by H. Scherzberg et al. describe the successful trials on a process involving reaction of MOP with sodium sulphate to produce the double salt glaserite (3K2SO4.Na2SO4). The glaserite is in turn reacted with MOP to produce SOP. The main disadvantage of the process is that it would be unsuitable for those who do not have access to such raw materials. Moreover, the process involves several complex unit operations including the need for chilling. Such processes have their limitation on large scale.
In a paper entitled ‘Duisberg's alternative to Mannheim’, Phosphorous & Potassium, 178, March-April 1992, p-20, by H. Scherzberg and R. Schmitz describe an integrated process for production of SOP from KCl and MgSO4 or Na2SO4. The main drawback of the process is that the amount of NaCl in raw materials has a critical effect on the process and, as such, would be less applicable to crude mixed salt as obtained from sea bittern. Another disadvantage is that the process involves heating and cooling which makes it energy intensive. Yet another disadvantage is that the by-product obtained is MgCl2 in concentrated solution form which has a limited market and lower appeal compared to low B2O3 containing Mg(OH)2 solid produced as part of the integrated process of the present invention. In a paper entitled ‘Mixed Salt from Sea Bittern’, Salt Research & Industry, 2, 126-128, 1969 by G. D. Bhatt et al. have described the process of manufacture of mixed salt, i.e., comprising a mixture of NaCl and kainite (KCl.MgSO4.3H2O), from sea bittern through solar evaporation and fractional crystallisation.
In a paper entitled “Preparation of syngenite from mixed salt in pure form in Salt Research & Industry, Vol. 6, No. 14, 1969 by K. P. Patel. and the paper entitled “Potassium Sulphate from Syngenite” by K. P. Patel, R. P. Vyas and K. Seshadri, in Salt Research & Industry, Vol. 6, No. 2, April 1969, wherein a process for preparation of SOP by leaching syngenite (K2SO4.CaSO4.H2O) with hot water and then recovering it by solar evaporation is described. The main drawback of the process is that it is energy intensive. Moreover, production of syngenite from mixed salt is itself an involved affair.
In a paper entitled “Manufacture of Potassium chloride and byproducts from Sea Bittern” by K. Seshadri et al. in Salt Research and Industry, April-July 1970, Vol 7, page 39-44, wherein mixed salt (NaCl and kainite) obtained from bittern is dispersed with high density bittern in proper proportion and heated to a temperature of 110° C. when kieserite (MgSO4.H2O) is formed which is separated by filtering the slurry under hot conditions. The filtrate is cooled to ambient temperature, when carnallite crystallizes out. Carnallite is decomposed with water to get a solid mixture of sodium chloride and potassium chloride while magnesium chloride goes into solution. Solid mixture of potassium chloride and sodium chloride is purified using known techniques to produce pure potassium chloride. The drawbacks of this process are that it fails to make use of the sulphate content in bittern and, instead, offers an elaborate process for manufacture of MOP, which, in any case, is inferior to SOP as fertilizer.
US Patent Application Number 2003 0080066 dated Oct. 29, 2001 by Vohra, Rajinder N. et. al. wherein an integrated process is revealed for recovery of high purity salt, potassium chloride, and end bittern containing 7.5 gpl Bromine. The process is based on desulphatation of brine with distiller waste of soda ash industry or calcium chloride generated from limestone and acid. The main drawback of the patent application is that the process is less attractive when distiller waste is not available in the vicinity and the process becomes less economical when carnallite has to be obtained from bittern without production of industrial grade salt. Moreover, as in the case referred to above, it is desirable to utilize the sulphate content in bittern and produce SOP in preference to MOP.
In a paper entitled ‘Great Salt Lake—A fertile harvest for IMC’ in Phosphorus & Potassium, 225, Jan-Feb, 2000. by Michael Freeman, have described the process which comprises of concentrating the brine containing 0.2-0.4% KCl, harvesting mixed salt, separation of high sodium chloride fraction through floatation, leaching with sulphate rich brine to produce schoenite, hot water dissolution of schoenite, fractional crystallization of SOP and recycling of mother liquor containing up to 30% of original K to evaporation pond. The main drawbacks of the process are: (i) the need for floatation which involves use of organic chemicals whose disposal is problematic, (ii) need for external heat for the purpose of recovery of SOP from schoenite through fractional crystallization at elevated temperature, (iii) need for recycling of as much as 30% of K to evaporation ponds where again it gets contaminated with other components of the brine.
In Ullmann's Encyclopedia of Industrial Chemistry, Sixth Edition, 1999, under the Chapter, Potassium compounds, a description of a process for production of SOP in Sicily is detailed. Kainite (KCl.MgSO4.2.75 H2O), is obtained from a potash ore by flotation. It is then converted into schoenite at ca. 25° C. by stirring with mother liquor containing the sulfates of potassium and magnesium from the later stages of the process. Schoenite is filtered off and decomposed with water at ca. 48° C. This causes magnesium sulfate and part of the potassium sulfate to dissolve and most of the potassium sulfate to crystallize. The crystals are filtered and dried. The sulfate mother liquor is recycled to the kainite—schoenite conversion stage. The main drawbacks of the process are that there is no mention of the fate of the mother liquor obtained upon conversion of kainite into schoenite which would inevitably entail considerable loss of K, and the need for external source of heat to effect the fractional crystallization of SOP.
Chinese patent CN 2000-112497, 29 Aug. 2000, by Song, Wenyi; et al., entitled “Method for preparing K2SO4 from sulphate type K-containing bittern.” The method comprises concentrating the bittern, separating NaCl, concentrating to obtain crude K-Mg salt containing 10-45% NaCl, crushing, mixing with saturated bittern to obtain a solution with concentration of 20-40%, removing NaCl by back-floatation, concentrating, dewatering to obtain refined K—Mg salt containing less than 5% NaCl, mixing the K—Mg salt and water at specified ratio, allowing the mixture to react at 10-60° F. for 0.5-3 hr, separating to obtain schoenite, mixing with KCl and water at specified ratio, allowing the mixture to react at 10-70° F. for 0.25-3 hr and separating to obtain K2SO4. The drawbacks of the process are (i) need for elaborate method of purification of mixed salt that includes removing NaCl by the less desirable method of back floatation that involves use of organic chemicals, (ii) lack of any mention of the manner in which the various effluent streams are dealt with, and (iii) dependence on outsourced KCl since no mention is made of any process for KCl production as part of the process.
In a paper entitled “Extraction of Potash and other Constituents from sea water Bittern” in Industrial and Engineering Chemistry, Vol. 10, No. 2, 1918, pp 96-106, by J. H. Hildebrand wherein theoretical aspects of the recovery of potash from sea bittern are described and a process for extraction is proposed. According to this process, bittern is evaporated at a temperature between 100-120° C., thereby forming a solid mixture of sodium chloride and kieserite (MgSO4.H2O), separating this mixture under hot conditions in a heated centrifuge, and cooling the mother liquor in a cooler for separation of carnallite. Carnallite is decomposed and washed with water to produce potassium chloride. The drawback of this process is that it is demanding in terms of energy requirement and sufficiently pure carnallite cannot be obtained. The main drawback of the process is the contamination of kieserite with NaCl which would necessitate further purification to obtain products in saleable form. Another drawback of the process is that it requires energy to remove sulphate from bittern in the form of kieserite whereas it would be preferable to utilize the sulphate for the production of SOP.
In yet another paper entitled “Production of Potassium Sulphate from Mixed Salt” in Salt Research & Industry, Vol. 2, No. 4, October 1965, by D. J. Mehta et al. describes a process of floatation technique for the production of potassium sulphate from two types of mixed salt available from the salt works of the Little Rann of Kutch is described. The process suffers from the drawback of lack of suitability when high sulphate containing sea bittern is used and the need for froth floatation, which is costly, cumbersome and polluting.
In Ullmann's Encyclopedia of Industrial Chemistry, Sixth Edition, 2002 (Electronic Version) dealing with Magnesium Compounds written by Margarete Seeger, Walter Otto, Wilhelm Flich, Friedrich Bickelhaupt and Otto. S. Akkerman, wherein the process of preparation of magnesium hydroxide from seawater is described. It is mentioned therein that preparation of low boron containing magnesia requires over liming of the seawater up to pH 12 to maintain B2O3 content less than 0.05% in magnesia. Over liming involves higher lime cost, need for neutralization of supernatant and results in a colloidal suspension which is not easy to filter. Another drawback is a lack of application of calcium chloride-containing effluent, which is discharged back into the sea.
Reference may be made to the Canadian patent entitled, “Process for the manufacture of potassium sulphate by treatment of solution containing magnesium chloride and potassium chloride”, application No. 423211, CA 1203666, by Wendling et al. wherein a process for the production of potassium sulphate from solutions containing magnesium chloride, such as solutions of carnallite ore and, in particular, the equilibrium mother liquors of a unit for the treatment of carnallite is described. According to this process, sodium sulphate and potassium chloride are added to the solutions containing magnesium chloride, so as to precipitate sodium chloride and schoenite, K2SO4MgSO46H2O, and the schoenite obtained is treated in a known manner to produce potassium sulphate. The main drawback of the process is the need to outsource sodium sulphate and the lack of any mention of a solution to the problem of KCl loss in effluent streams.
In a paper entitled “Recovery of Potassium Salts from Bittern by Potassium Pentaborate Crystallisation' in Separation Science & Technology, 31(6), 1996, pp. 857-870, by H. Gurbuz et al wherein sodium pentaborate is prepared from the reaction of Tincal and recycled H3BO3 in presence of water and thereafter treated with bittern to selectively precipitate out potassium pentaborate, which in turn is acidulated with sulphuric acid and fractionally crystallized to remove K2SO4 and recycle the H3BO3 in the process. The main drawbacks of the process are that the mother liquor contains significant quantities of boron which entails elaborate procedure to recover boron and, moreover, the MgO obtained from such mother liquor would be unfit for industrial use. Moreover, although such a process can still be thought of for sulphate poor bittern, it would not be a preferred route when the bittern is rich in sulphate content. Yet another drawback is the need to chill the acidulated product for high yield.
In a paper entitled “Henry's constant for Bromine-Sea Brine systems and liquid film mass transfer coefficient for desorption of bromine from sea brine” by A. S. Mehta in Indian Chemical Engineer, 45(2), 2003, p. 73, wherein the author describes the process of bromine manufacture from bittern. Bittern is acidified with sulphuric acid to a pH of 3.0-3.5 and the bromide ion is then oxidized with chlorine and stripped off with the help of steam. The acidic de-brominated bittern is neutralized with lime, the sludge thus formed removed, and the effluent discharged. Reference may also be made to bromine plants located in the vicinity of natural salt beds in the Greater Rann of Kutch in Gujarat, India that utilize natural bittern for bromine production by the above method and discharge their effluent back into the Rann. Disposal of sludge poses a formidable challenge in these plants.
In a paper entitled “Improved Treatment of Waste Brines” by Chr. Balarew, D. Rabadjieva and S. Tepavitcharova, (International Symposium on Salt 2000, page 551-554) for recovery of marine chemicals. The authors describe the use of lime for precipitation of Mg(OH)2 from a part of available bittern, and desulphatation of balance bittern with the resultant CaCl2 solution for recovery of KCl via carnallite. The authors have not discussed any scheme of utilizing such methodology for production of SOP from sulphate-rich bittern. Moreover, as will be evident later, Mg(OH)2 produced directly from raw bittern has much higher B2O3 content compared to Mg(OH)2 prepared from the Mg2+ source of the present invention, which is linked to production of SOP.
Chinese Patent No. 1084492 assigned to Lu Zheng describes the process of manufacture of SOP from bittern and potassium chloride. In this process, bittern is processed by evaporation, cooling, floatation and then it is reacted with potassium chloride to make potassium sulfate and by-products of industrial salt and residual brine. The main drawbacks of this process are that it requires involved separation techniques like floatation to remove NaCl from mixed salt and KCl required for production of SOP from schoenite has to be procured separately. Moreover, although overall yield in terms of potash recovery is 95%, yield with respect to such procured KCl is not mentioned.
In a WO patent application No: PCT/IN03/00463, 2003 by P. K. Ghosh et al describes the process of manufacture of SOP from bittern and MOP. In this process, kainite-type mixed salt was produced by evaporation of sea bittern and the mixed salt was then treated with water (and also K+-rich liquor obtained during schoenite into SOP) to obtain schoenite and a by-product liquor (SEL) containing sodium, potassium and magnesium salts. This liquor is then treated with CaCl2 to eliminate sulphate and then evaporated to produce carnallite which is then decomposed and hot leached to obtain KCl in solid form. The schoenite is then treated with KCl and water to obtain SOP and a filtrate that can be recycled in the step involving conversion of kainite mixed salt into schoenite. The drawback of this process is that the production of KCl from SEL through carnallite intermediate is lengthy, involves co-generation of Mg(OH)2, and requires evaporation of large amounts of water. Thus while it is useful to generate KCl from waste, an improved process would be highly desirable.
In a paper entitled “Study of the Competitive Binding of Mixed Alkali and Alkali Earth Metal Ions using Dibenzo-30-Crown-10” (Polyhedron 2005, 24, pp. 1023-1032) by P. Agnihotri et al. wherein potassium rich bitterns were treated with the crown ligand to extract out potassium selectively. Reference is also made to other references contained in the paper. The drawbacks of the process are the relatively low selectivity of these ligands and difficulties around regeneration of the ligand.
In a paper entitled “The quantitative determination of potassium with hexanitro diphenylamine (dipicryal amine)” in Angewandte Chemie, 49(46), pp 827-30, 1936 by A. Winkel et al. In this method Mg-dipicryalaminate, which is highly soluble in water, is used to prepare insoluble K-dipicryalaminate. The main draw back of this process is that the inventors have not revealed the recovery of K+ and recycling of dipicryalamine (DPA) from K-dipicryalaminate.
Australian patent AU 109552, 1940 “Potassium salts”, assigned to J. Kielland, describes the recovery of potassium from brine with the aid of dipicrylamine. Ca2+ salt of dipicrylamine was added to brine, the precipitated K-dipicrylaminate is separated and treated with mineral acids, which liberated dipicrylamine for further use. The drawbacks of this process are that no distinct advantage in undertaking such extraction is disclosed.
German patent DE 726545, 1942 “Extracting potassium from dilute solutions, e. g., sea water”, assigned to E. Berner, and J. Kielland, describes the use of highly nitrated, secondary aromatic amines, e. g, hexanitromethyldiphenylamine or pentanitromethyldiphenyl-amine for the extraction of potassium. The drawbacks of this process are that isolation of solid salt from the dilute aqueous solution is energy intensive and no definite advantage was undertaken for direct use of the aqueous solution.
Great Britain patent No GB 605694, 1948 “Recovery of potassium salts” describes the process of recovery of K+ salt from sea water using dipicrylamine. Sea water was treated with a solution of Ca-dipicrylaminate, whereby insoluble K-dipicrylaminate was filtered and treated with a mineral acid such that the K+ goes into solution while dipicrylamine remains as solid, which was recycled. The main drawback of this process is that there is no report to use this methodology for the preparation of KCl solution for the explicit purpose of utilizing it for SOP production.
In a paper entitled “Extraction of potassium salts from saline mother liquors by hexanitrodiphenylamine. II”, Ann. Chim. (Rome), 51, pp 645-55, 1961. by F. Massazza, and B. Riva, the extraction of potassium salts from saline mother liquors by hexanitrodiphenylamine is described. The precipitated K-dipicrylaminate was treated with HNO3, which formed KNO3 and regenerated dipicryalamine. The main drawback of this process is that it has been exclusively used for the preparation of potassium nitrate and no report to use of this methodology for preparation of aqueous KCl to use it for SOP production.
In a paper entitled “Selective extraction of potassium from sea water, bitterns, and mixed salts”, Technology (Sindri, India), 3(4), 177-83, 1966, by J. N. Kapoor, and J. M. Sarkar, the extraction of K+ from sea water, bitterns, and mixed salts using Mg-dipicrylaminate is described. Mg-dipicrylaminate produces precipitate of K-dipicrylaminate, the chelating agent is then regenerated with HNO3, also forming KNO3. The main drawback of this process is that no report to use of this methodology for preparation of aqueous KCl for its direct application for the production of SOP.
In a paper entitled “Recovery of potassium from sea water and salt bittern with dipicrylamine”, Huaxue, 4, pp 106-11, 1969 by S.-K. Chu, and C.-T. Liaw, the recovery of K+ as chelate compound of dipicrylamine from artificial sea water, natural sea water, and salt bittern as described. Recovery of dipicrylamine was best achieved by adjusting pH of the solution below 3. The main drawbacks of this process are that no report for utilization or isolation of the K+ salt and recycling of DPA.
In a paper entitled “Potassium from sea water—a daring venture”, Chemistry and Industry, 13th November issue, pp 1309-1313, 1971. by J. Kielland has described the process of recovery of K+ as K-dipicrylaminate by adding Ca-dipicrylaminate into sea water. The precipitated K-dipicrylaminate is treated with HNO3 to form a KNO3 solution and insoluble dipicrylamine is recycled. The main drawbacks of this process are that KNO3 has no use for production of SOP and there is no report for generation of aqueous KCl following the same methodology.
In a paper entitled “Recovery of potassium from concentrated sea water with dipicrylamine”, in Nippon Kaisui Gakkaishi, 32(2), pp 82-8, 1978. by M. Matsuda et al. the recovery of K+ from concentrated brine as described. Na+ salt of dipicrylamine anion was added into concentrated brine to precipitate K+ salt of dipicrylamine, which was then reacted with HNO3 to form KNO3 and dipicryalamine was precipitated. The main drawbacks of this process are that KNO3 has no use for production of SOP and there is no report for generation of aqueous KCl following the same methodology.
In a paper entitled “Recovery of potassium using magnesium dipicrylaminate” in Chemical Era, 14(8), pp 290-6, 1978. by M. Y. Bakr et al. the process of recovery of K+ as K-dipicrylaminate by adding Mg-dipicrylaminate into bitterns as described. The precipitated K-dipicrylaminate is treated with HNO3 to form a KNO3 solution and insoluble dipicrylamine. The main drawback of this process is that the focus has been exclusively on preparation of potassium nitrate by the above technique and no report to use of this methodology for preparation of KCl solution for the purpose of utilizing it for SOP production.
In a review article entitled “Recovery of potassium using magnesium dipicrylaminate”, Chemical Economy & Engineering Review, 11(1-2), pp 31-5, 1979. by M. Y. Bakr et al. set described the reaction conditions for recovery of KNO3 from K-dipicrylaminate. K-dipicrylaminate obtained from extraction of K+ from Egyptian bitterns is decomposed by HNO3 solutions at different conditions to determine the best conditions for recovery of KNO3 and dipicrylamine for recycle. The main drawbacks of this process are that KNO3 has no use for the preparation of SOP and there is no report to exploit this methodology for generation of aqueous KCl, which can be used for SOP production.
In a paper entitled “Towards Understanding of the Selective Precipitation of Alkali Metal Cations in Presence of Dipicrylamine Anion” (Eur. J. Inorg. Chem., 2005, pp. 2198-2205), by E. Suresh et al. describes the causes underlining the selectivity of dipicrylamine towards different ions have been unraveled and, in particular, the high selectivity towards K+ in bittern systems has been explained.